The present invention relates to cellular telecommunication systems. More particularly, and not by way of limitation, the present invention is directed to an apparatus and method for balancing a traffic load between multiple radio cells.
In existing 1x Evolved-Data Optimized (1x-EV-DO) advanced networks, a Network Load Balancing (NLB) algorithm provides methods of off-loading traffic from more loaded radio cells to less loaded radio cells by manipulating allowed forward/downlink Base Transceiver Station (BTS) sectors from an Active Set (A_SET), for every active over-the-air connection. The NLB algorithm utilizes the measured load on BTS sectors in the A_SET and forces an Access Terminal (AT) to get service from a less loaded sector. This is done by having the Radio Network Controller (RNC) or Base Station Controller (BSC) unlock a Data Rate Control Lock (DRCLock) bit in a serving downlink (DRCLock=0), which forces the AT to select a different serving downlink sector among the pilots from the A_SET.
Although helping to balance the traffic load and improve capacity and individual user throughput, the NLB algorithm may degrade existing radio connection Key Performance Indicators (KPIs) for several reasons. First, since the algorithm moves ATs from preferred downlink sectors to possibly less optimum sectors, this may lead to degraded connection loss statistics. The connection drop rate is an important KPI that network operators use to measure overall health of the over-the-air connectivity. Degradation of this KPI could invalidate capacity gains and prevent successful NLB implementation.
Second, the NLB algorithm requires periodic Route Update reports from the ATs so that the algorithm can consider current RF signal quality when making its balancing decisions. There is no option to set periodic reporting in 1x-EV-DO, so Route Update Messages have to be solicited to get the reports. This puts additional strain on the call processing entity at the RNC, and needs to be minimized without compromising the ability of the NLB algorithm to gauge the signal strengths of forward/downlink pilots in the A_SET.
Third, the NLB algorithm must have a correct set of NLB metrics to determine whether moving a given AT from one downlink sector to another will do more harm than good due to adverse effects on other ATs. Without mechanisms for obtaining these metrics, the NLB algorithm may degrade Signal-to-Noise Ratio (SNR) and Quality of Service (QoS) for larger numbers of ATs.